Optical Coherence Tomography (hereinafter also referred to as “OCT”) is a method for measuring a tomographic image of a living body using optical coherence, and is widely used for obtaining two-dimensional/three-dimensional tomographic images of corneas and retinas especially in the field of ophthalmology. Commonly, in OCT, two-dimensional images are called B-scan images, and three-dimensional images are called C-scan images. Therefore, a two-dimensional image is called a B-scan (graphical) image, and a three-dimensional image is called a C-scan (graphical) image, hereinafter.
Typically, a device for taking tomographic images of a subject eye is provided with, in addition to an OCT optical system, an optical system for obtaining other front images of an eye (e.g., front images of eye fundus and front images of cornea surface). For example, fundus cameras or Scanning Laser Ophthalmoscope (SLO) are employed for imaging of front images of eye fundus. The front images taken by a fundus camera or an SLO is used in observation of a configuration of an entire cornea or retina, in positioning when obtaining a tomographic view in OCT, and in correction of positional displacement of an obtained OCT image.
If a subject eye moves during OCT imaging, motion artifact is produced in an OCT tomographic image that has been obtained, and it is not possible to obtain an accurate OCT tomographic image. Therefore, conventionally, front images taken by a fundus camera or an SLO are used to calculate a moving distance of the subject eye, and thus tracking in the OCT imaging or correction of positional displacement in an obtained OCT image is performed using the calculated moving distance.
Japanese Publication No. 2008-029467 discloses one example of the above. Specifically, even if the subject eye moves during measurement, it is possible to observe a certain tomographic view (B-scan image) without any influence of the movement by switching irradiation every time a single OCT B-scan graphical image is obtained to obtain an SLO eye fundus image, and correcting positional displacement of an OCT B-scan graphical image using the obtained SLO eye fundus image.